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Strange siphoning issue during fermentation. Need some pro help

I ferment in a 7 gal SS Brewtech brew bucket. I have the domed lid, the 3" tri-clamp cap that I secure with a tri-clamp. Out of the top of the cap, I have a 90-degree elbow with a 1/2" hose barb, and a 1/2" silicon blowoff tube that I put into a 3 cup mason jar full of liquid. All of that goes inside a minifridge so I can dial in the temp. It is easy to use, and easy to clean setup. Here is my problem…

When I lower the temp in the fridge to lager or cold crash, my system acts like a siphon a starts sucking up the liquid in the mason jar. I know there is going to be a density change when I lower the temp, but not this much. The fermentor is sucking up about 2 cups every 2-3 days.

What the heck is happening? And how can I stop it?


Just cap it off. You dont need the santizer any more.

What type of liquid are you sucking Into your bei

That is an idea I hadn’t thought of. I suppose even if I’m lagering, the bucket should be able to take a small amount of pressure that might form during the end of fermentation. Right?

Star San or water.

Correct. It shouldn’t pull enough vacuum to implode the tank. I would try going slow, 5° in the morning and in the evening until you get to your temps.

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The vacuum is reabsorption of Co2 into your brew as it chills down the amount in you head space is little but enough to pull sanitizer back through the line but not enough to damage your bucket by just capping it off. Make sure it is a air tight seal so you don’t pull oxygen in


Or if you want to get super fancy you could hook up a CO2 source at about 2psi and cold crash. Once it hits your temp turn the CO2 off. As the vacuum occurs it will pull in the CO2.


I use Anvils brew buckets and have very close to the same setup as you… The way I handle my end of fermentation is to allow the fermenter come up to say… 70*… It’ll sit for a week ( I’m not in a rush) then I push the brew out with CO2 into a keg… I push about 40 PSI’s to seat the lid then put it in for cold aging… IF I feel the need to, I can add more CO2… Sneezles61

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